Right Atrial Pacing Research Articles

A shortened electrocardiographic diastolic interval is involved in diastolic dysfunction and HFpEF

Abstract Background Heart failure with preserved ejection fraction (HFpEF) is a clinical syndrome characterized by left ventricular diastolic dysfunction (LVDD). We hypothesized that a short electrocardiographic diastolic time predisposes to LVDD and HFpEF by deteriorating diastolic function. This effect may be more pronounced in women than men, given longer QT interval in women. Methods To experimentally test if incremental shortening of the diastolic interval indeed worsens the diastolic function, we shortened electrical diastole using right atrial (RA) pacing and QT-prolonging medication (sotalol) in six pigs. We used 12-lead ECG and echocardiography to assess electrical diastole (TQ interval) and diastolic function. We next analyzed electrocardiograms and corresponding information on LVDD and HF in electronic health record data from 85,145 patients that visited one of 13 Cardiology Centers of the Netherlands. We sex-specifically assessed the association between TQ interval on the one hand and LVDD or HFpEF on the other. Results In pigs, baseline TQ interval was 257 (±SD 66) ms, which decreased to 232 (±SD 36) ms during RA pacing (100 bpm), and further to 193 (±SD 52) ms with concomitant sotalol administration (2 mg/kg iv, bolus). These changes in TQ interval resulted in reversal of E/A ratio, with a significant correlation between TQ interval and decreasing e’/a’ ratio (r=0.382, p=0.024) (Figure 1). In patients who underwent cardiac evaluation with ECG and echocardiography, diastolic abnormalities were documented as LVDD (n=26,009 (30%)) and HFpEF (n=2,551 (3%)). TQ intervals were significantly shorter in patients with LVDD and HFpEF (479 (±SD 128) and 485 ms (±SD 138), respectively) compared to the ones without LVDD or HFpEF (523 (±SD 137) ms). A shorter TQ interval increased the risk for having LVDD and HFpEF when adjusted for confounders (LVDD; ORadjusted= 1.37 (95% CI: 1.28, 1.45), HFpEF; ORadjusted= and 1.16 (95% CI: 1.01, 1.35) (Table 1). There was significant sex-interaction (p= 0.039) for TQ and LVDD risk, with stronger associations in women (ORadjusted= 1.43 (95% CI: 1.32, 1.56) compared to men (ORadjusted= 1.35 (95% CI: 1.10, 1.64) (Table 1). Conclusion Experimentally decreasing the electrical diastolic interval leads to diastolic function abnormalities in pigs. In humans, a shorter diastolic interval is associated with a higher risk of having either LVDD or HFpEF. Our findings imply that a shortened electrical diastolic interval may precede diastolic dysfunction and HFpEF. Therefore, prolonging or preserving electrical diastole may be effective in preventing or treating HFpEF, especially in women.Figure 1Table 1

PO-03-074 INITIAL HEART RATE SCORE IS PREDICTOR FOR OCCURRENCE OF NEW ATRIAL FIBRILLATION INDEPENDENT OF WELL-KNOWN RISK FACTORS AND RELATES TO RIGHT ATRIAL PACING RATE IN PACEMAKER PATIENTS

Heart Rate Score (HRSc), the percent of right atrial (RA) beats in the largest paced or sensed 10-bpm histogram bin, predicts survival in ICD and CRT-D patients without atrial fibrillation (AF). For pacemaker (PM) patients, although age, gender and RA and right ventricular pacing percent (% RA and RV pacing) have been related to AF, the relationship of HRSc to subsequent AF is unknown. To evaluate the relationship between initial post implantation HRSc and incidence of newly developed AF, and well-known predictors for AF in PM patients. Patients with dual-chamber, atrial tracking PMs, implanted 2013-2017, who had ALTITIUDE remote monitoring data available, were included. HRSc was determined from histogram data during the first 3 months post-implant. Only patients with ≥600,000 beats of histogram data collected at baseline were included. Patients with single-chamber or biventricular PMs were excluded. Patients were excluded if they had AF, defined as atrial high rate episodes >5 minutes or >1% of RA beats >170 bpm during the initial 3-months post-implant. AF after the baseline period was evaluated by the definition: >1% of atrial beats >170 bpm. Sinus node disease (SND) was defined as needed for RA pacing ≥ 40% and atrio-ventricular block (AVB) as needed for right ventricular pacing ≥ 20% during the baseline period. Of the total population (N=34,543), 15,252 patients had device-determined SND and 16,190 patients had AVB. Utilizing multivariable analysis, the initial HRSc (HR: 1.07, 95% CI: 1.05-1.09; P<0.0001) independently predicted subsequent AF after adjusting for age, gender, % RV pacing and rate-response programming. Patients with initial HRSc≥70% were older, and had higher % RA pacing, lower % RV pacing and were more likely programmed with rate-response vs subjects with initial HRSc<70%. There was a direct, and significant, increase in new-onset AF with each 20% increment in HRSc and/or % RA pacing (both P<0.001, Figure) during median of 2.8 (1.0-4.0) years follow-up. The %RA pacing and initial HRSc were strongly correlated (Pearson correlation coefficient=0.9). % RV pacing did not predict AF. Both SND patients and AVB patients with initial HRSc≥70% had a significantly increased risk of AF (log-rank P <0.001) compared to patients with HRSc<70%. Initial HRSc, strongly related to percent RA pacing, predicts subsequent AF independent of well-known risk factors in both device-determined SND and AVB.

PO-04-086 IMPLANTATION OF A LEADLESS PACEMAKER FOR HYBRID DUAL CHAMBER PACING IN A PATIENT WITH A FAILING RIGHT VENTRICULAR LEAD AND HIGH SURGICAL RISK: A CASE REPORT

Mechanical atrial sensing in Micra AV (Medtronic) leadless pacemakers facilitates atrioventricular (AV) synchrony in patients with AV block despite single chamber pacing. Little data is available on the efficacy of Micra AV atrial tracking in patients with concomitant sinus node dysfunction requiring atrial pacing. We present a case that demonstrates the efficacy and utility of Micra AV pacing in the context of transvenous atrial pacing. N/A A 49-year-old woman with complete heart block, sinus node dysfunction, right-sided dual-chamber pacemaker, and subsequent right atrial (RA) lead dysfunction treated with RA lead capping and new implantation, presented to our institution for pacemaker management. Device interrogation revealed rising RV lead impedances and pacing thresholds, for which lead extraction and re-implantation was recommended. Pre-operative imaging revealed partial flow obstruction in the right subclavian vein, an interrupted inferior vena cava, and a persistent left superior vena cava (SVC) with no right SVC connection. As urgent intra-operative cardiopulmonary bypass in the event of vascular rupture would prove difficult, the patient was deemed not a candidate for lead extraction. In an effort to prevent SVC syndrome, the decision was made to implant a Micra AV leadless pacemaker and program the old RV lead to off. The patient’s anatomy precluded a conventional femoral venous approach to Micra implantation, so implantation was achieved via the right internal jugular vein. The procedure was successful without intraprocedural complication. To allow for atrial pacing and to promote AV synchrony, the dual chamber pacemaker was programmed to AAIR 70/100 bpm with the leadless pacemaker programmed to VDD 50/105 bpm. Quarterly device interrogations in the 12 months following Micra implantation demonstrated 77-92% RA pacing and 99% RV pacing with atrial tracking from the Micra device at 76-83% with optimized atrial sensing. This case exemplifies the clinical scenario in which hybrid dual chamber pacing may be indicated. The case also highlights the atrial tracking capability of the Micra AV leadless pacemaker in the setting of an AAIR transvenous pacemaker, ultimately demonstrating the feasibility and potential application of hybrid dual chamber pacing in patients in need of RV lead revision but with prohibitive surgical risk or limited venous access.

Benefit of right inferior pacing on conduction across Bachmanns Bundle

Abstract Background Bachmann's Bundle (BB) is the main preferential route for interatrial conduction and plays an important role in initiation and perpetuation of atrial tachyarrhythmia such as atrial fibrillation (AF). Especially in patients with inter- and intra-atrial conduction disorders, the conventional site for placement of right atrial (RA) pacing lead in the RA appendage (RAA) has been questioned as it results in a higher incidence of AF. However, it remains unknown how pacing from various sites affects conduction at BB. Purpose To examine the impact of programmed stimulation from the left and right atrium on activation and electrophysiological features of BB. Methods Intra-operative high-resolution epicardial mapping of BB was performed during sinus rhythm (SR) and programmed stimulation in 32 patients (29 male, 65±10 years). Programmed stimulation included a fixed rate sequence of average SR cycle length minus 50 ms provided from the RAA, junction of the RA with inferior caval vein (RAinf) and left atrial appendage (LAA). Electrophysiological features included unipolar voltage, conduction velocity, potential type (single, short/long double and fractionated) and conduction delay/block (CDCB). Results The average cycle length during SR was 962 [869–1085] ms. Pacing from RAA resulted in comparable activation patterns as during SR. As expected, pacing from LAA resulted in left-to-right conduction across BB. However, during pacing from RAinf in most patients activation started in the centre of BB. Compared to SR, the least amount of differences in electrophysiological features was found during pacing from the RAA, followed by pacing from RAinf and LAA. Unipolar voltages, conduction velocity and potential type distribution were similar. However, during pacing from RAinf, total activation time decreased compared to SR (44 [38–62] ms vs 60 [51–67] ms, P=0.012), while total activation time increased by pacing from LAA (66 [60–72] ms, P=0.020). The total activation time during pacing from RAinf was lower compared to LAA (P&amp;lt;0.001) and RAA pacing (P=0.001). During pacing from LAA, the amount of CDCB increased compared to SR (6.6 [4.1–9.9] % vs 8.7 [5.6–12.8] %, P=0.009), while there were no differences in CDCB between SR and pacing from both RAA and RAinf. Reduction of CDCB was most often achieved during pacing from RAinf (12 patients), especially in patients who already had a higher amount of CDCB during SR (8.0 [7.3–11.2] % vs 4.3 [3.0–5.9] %, P&amp;lt;0.001). Reduction of both CDCB and total activation time was achieved in 10 patients by pacing from RAinf, while only 6 patients benefitted from RAA pacing. These patients had similar amount of conduction disorders. Conclusions Pacing from the inferior RA results in a remarkable decrease of total activation time and conduction disorders compared to pacing from the LAA or RAA. As specific patients may benefit more from inferior RA pacing, locations for pacing lead placement should be individualized. Funding Acknowledgement Type of funding sources: None.

BI-ATRIAL MAPPING AND ELEVATED HEART RATES IDENTIFY ABNORMAL ATRIAL SUBSTRATE IN ATRIAL FIBRILLATION PATIENTS WITHOUT LOW-VOLTAGE AREAS IN THE LEFT ATRIUM

BI-ATRIAL MAPPING AND ELEVATED HEART RATES IDENTIFY ABNORMAL ATRIAL SUBSTRATE IN ATRIAL FIBRILLATION PATIENTS WITHOUT LOW-VOLTAGE AREAS IN THE LEFT ATRIUM

PO-688-04 LOW RIGHT ATRIAL PACING USAGE IN CARDIAC RESYNCHRONIZATION THERAPY POPULATION - DESCRIPTIVE STUDY FROM THE CERTITUDE REGISTRY

Two-lead cardiac resynchronization therapy with DX technology (CRT-DX) has been demonstrated to provide adequate resynchronization therapy equivalent to conventional three-lead CRT-D systems with fewer complications. We performed a retrospective review of right atrial (RA) lead pacing usage in our CRT-D population to identify potential patients with low atrial pacing percentage (Ap%) that may benefit from a two-lead CRT-DX system. We identified and characterized CRT-D and CRT-DX systems with at least 3-months of follow-up duration from the CERTITUDE registry, a de-identified database containing qualified US BIOTRONIK devices registered with Home Monitoring®. CRT-D generators with an implanted RA pacing lead and right ventricular ICD lead were classified as CRT-D systems. CRT-DX systems were classified as having DX technology with a DX ICD lead and no RA lead implanted. All Ap% and p-wave sensing values from daily remote monitoring transmissions were analyzed from these groups. We defined Low Ap Usage as a mean Ap% ≤5% and no presence of daily Ap% ≥9% with the understanding that defining the true need for atrial pacing would require consideration of individual programmed parameters, diurnal variation, dependency status, etc. A total of 4,903 systems (4,516 CRT-Ds, 387 CRT-DXs) were identified for analysis with a mean follow-up duration of 954.7 days (SD: ±466.4). Of the 4,516 CRT-D systems analyzed, 902 (20.0%) had Low Ap Usage. Of the 387 CRT-DX systems analyzed, 8 systems (2.1%) subsequently required a right atrial lead implant with a mean time to RA implant of 601.4 days (SD: ±431.3). Mean sensing values were higher in the CRT-DX group with p-wave amplitude of 3.42 mV compared to 3.11 mV (p-value<0.001) in the CRT-D group. In this descriptive analysis from the CERTITUDE registry, we identified 20.0% of the CRT-D patients with low right atrial pacing usage, which highlights a proportion of CRT subjects that could be good candidates for a CRT-DX system. Additionally, the need for atrial pacing in CRT-DX patients was uncommon. Lastly, atrial sensing parameters with CRT-DX were superior as compared to the CRT-D group.

Noninvasive assessment of intraventricular pressure difference in left ventricular dyssynchrony using vector flow mapping.

Diastolic intraventricular pressure difference (IVPD) reflects left ventricular (LV) diastolic function. The relative pressure imaging (RPI) enables the noninvasive quantification of IVPD based on vector flow mapping (VFM) and visualization of regional pressure distribution. LV dyssynchrony causes deterioration of cardiac performance. However, it remains unclear how IVPD is modulated by LV dyssynchrony. LV dyssynchrony was created in ten open-chest dogs by right ventricular (RV) pacing. The other ten dogs undergoing right atrial (RA) pacing set at the similar heart rate with RV pacing were used as controls. Echocardiographic images were acquired at baseline and during pacing simultaneously with LV pressure measurement by a micromanometer. Pressure difference (ΔP) was computed between the apex and the base of the LV inflow tract during a cardiac cycle by RPI and ΔP during isovolumic relaxation time (ΔPIRT), a parameter of diastolic suction, and that during early filling phase (ΔPE) were measured. During RV pacing, stroke volume (SV) and ΔPIRT decreased significantly, while ΔPE did not change compared to the baseline. During RA pacing, SV, ΔPIRT and ΔPE did not change significantly. ΔPIRT tended to correlate with -dP/dtmin and end-systolic volume, and significantly correlated with ejection fraction. IVPD during isovolumic relaxation time was decreased by LV dyssynchrony, while IVPD during early filling phase was not. A reduction of diastolic suction is observed in LV dyssynchrony and is significantly related to a decrease in SV.

Right Atrial Pacing to Improve Acute Hemodynamics in Pulmonary Arterial Hypertension

Pacing to increase resting heart rate (HR) is commonly employed in order to improve hemodynamics and cardiac output (CO), particularly in post-operative setting when right ventricle (RV) dysfunction is present. We tested if right atrial (RA) pacing improves RV hemodynamics acutely, and if the degree of baseline RV dysfunction modifies this relationship. We prospectively enrolled adult subjects with known or suspected pulmonary arterial hypertension (PAH) who underwent elective right heart catheterization between January 2013 and April 2016. RV pressure-volume (PV) analysis was performed with conductance catheters. RV volumes were calibrated by cardiac MRI same day. After measuring baseline PV data, a bipolar pacing wire was positioned in the RA and rate set to 80 to 90 beats per minute (bpm). Rate was increased in steps of 20 bpm. PV loops were recorded at end-expiration after 1 minute in each group: 80-99, 100-119, and 120-139 bpm. Parametric data were analyzed by Repeated Measures ANOVA, and non-parametric data were analyzed by Friedman Test. Baseline hemodynamic predictors of CO were analyzed by Repeated Measures simple linear regression. Twenty-three subjects were included in this analysis. Baseline mean RA pressure was 7 ± 3 mmHg with pulmonary vascular resistance of 5.2 ± 4.1 wood units. As HR increased with RA pacing, stroke volume (SV) declined in each pacing group (68±22, 61±19, 54±21 mL, respectively; p<0.001) with increase in CO (5.5±1.9, 6.2±1.9, 6.6±2.5 L/min; p<0.001). The dP/dt maximum increased (429, 490, 549 mmHg/s; p<0.001); however, RV-pulmonary arterial coupling (Ees/Ea) fell with pacing (0.97 vs 0.84 vs 0.78, p=0.009). No baseline hemodynamic parameter or measure of RV function modified the relationship between CO and RA pacing. Between-subject data had large variation; exclusion of non-PAH subjects (n=6) did not alter results. As heart rate increases with RA pacing, RV contractility and CO increase modestly at the expense of cardiac efficiency.

P619Stress-strain loop area better represents regional myocardial work than pressure-strain loop area in the dyssynchronous and remodelled left ventricle

Abstract Background Pressure-strain-loops (PSL) have been suggested as surrogate parameter of regional myocardial work. However, in left ventricles (LV) with inhomogeneous remodelling, e.g. due to left bundle branch block (LBBB), wall stress may be unevenly distributed. Stress-strain loops (SSL) include information on both regional wall thickness and curvature, and may therefore provide a better surrogate. Study plan We therefore compared the correlation of segmental myocardial work estimated through both PSL and SSL to segmental myocardial glucose metabolism as a gold standard, in an animal model of pacing-induced LV remodelling. Methods Twelve sheep developed LV dilatation, thinned septum and thickened lateral wall, due to eight weeks of rapid right-atrial and right-ventricular free wall (DDD) pacing (at 180 bpm), causing a LBBB-like dyssynchrony. Invasive LV pressure and echocardiographic speckle tracking based circumferential strain were used to construct PSL. SSL were calculated by considering in addition dynamic changes in segmental myocardial wall thickness and curvature using the formula of Laplace. 18F-fluorodeoxyglucose (FDG)-uptake was measured by positron emission tomography (PET) in absolute values as standardised uptake ratio (SUR). Spatial resolution of PET was improved by ECG- and breathing-gating and using anatomical priors. All imaging was performed during dyssynchronous DDD-pacing and synchronous AAI-pacing (right-atrial pacing only), at baseline (n=3 animals), and after eight weeks of pacing induced remodelling (n=12 animals). Results Both at baseline (Fig. A+B) and after 8 weeks (Fig. D+E), switching between AAI and DDD-pacing caused an acute re-distribution of regional myocardial work as measured by both PSL and SSL. In contrast to PSL, however, SSL identified more regional differences among walls in remodelled hearts and showed clearer regional changes when switching between AAI and DDD-pacing. The correlation between regional work, assessed by PSL and SSL, and metabolism by PET, was comparable at baseline (r=0.65 and r=0.64, respectively) (Fig. C). In remodelled hearts after 8 weeks, however, the correlation of regional work assessed by SSL and glucose uptake by PET was significantly higher compared to PSL (r=0.73 vs. r=0.59, respectively; p&lt;0.05) (Fig. F). Conclusions Regional myocardial work assessed by stress-strain loops correlates significantly better to regional metabolism as measured by PET glucose uptake, particularly after remodelling. Our findings therefore suggest that integrating information on wall thickness and curvature is essential for the reliable assessment of regional myocardial work, especially in dyssynchronous and remodelled left ventricles.

The Detrimental Effect of RA Pacing on LA Function and Clinical Outcome in Cardiac Resynchronization Therapy

ObjectivesThis study assessed the impact of right-atrial (RA) pacing on left-atrial (LA) physiology and clinical outcome. BackgroundData for the effects of RA pacing on LA synchronicity, function, and structure after cardiac resynchronization therapy (CRT) are scarce. MethodsThe effect of RA pacing on LA function, morphology, and synchronicity was assessed in a prospective imaging cohort of heart failure (HF) patients in sinus rhythm with a guideline-based indication for CRT. Additionally, in a retrospective outcome cohort of consecutive HF patients undergoing CRT implantation, the relationship to RA pacing was assessed using various outcome endpoints. High versus low atrial pacing burden was defined as atrial pacing above or below 50% in both cohorts. ResultsA total of 36 patients were included in the imaging cohort (68 ± 11 years of age). Six months after CRT, patients with high RA pacing burden showed less improvement in LA maximum and minimum volumes and total emptying fraction (p < 0.05). Peak atrial longitudinal strain and reservoir and booster strain rates but not conduit strain rate improved after CRT in patients with low RA pacing burden but worsened in patients with high RA pacing burden (p < 0.05 for all). A high RA pacing burden induced significant intra-atrial dyssynchrony (maximum opposing wall delay: 44 ± 13 ms vs. 97 ± 17 ms, respectively; p = 0.022). A total of 569 patients were included in the outcome cohort. After covariate adjustments were made, a high RA pacing burden was associated with reduced LV reverse remodeling (β = 8.738; 95% confidence interval [CI]: 3.101 to 14.374; p = 0.002) and new-onset or recurrent atrial fibrillation (41% vs. 22%, respectively, at a median of 31 months [range 22 to 44 months follow-up]; p < 0.001). There were no differences in time to first HF hospitalization or all-cause mortality (p = 0.185) after covariate adjustment. However, in a recurrent event analysis, HF readmissions were more common in patients exposed to a high RA pacing burden (p = 0.003). ConclusionsRA pacing in CRT patients negatively influences LA morphology, function, and synchronicity, which is associated with worse clinical outcome, including diminished LV reverse remodeling, increased risk for new-onset or recurrent AF and heart failure readmission. Strategies reducing RA pacing burden may be warranted.

Heart rhythm model for the simulation of electric fields in transesophageal atrial pacing and cardiac resynchronization therapy

Abstract Electric field of biventricular (BV) pacing, left ventricular (LV) electrode position and electrical interventricular desynchronization are important parameters for successful cardiac resynchronization therapy (CRT) in patients with heart failure, sinus rhythm and reduced LV ejection fraction. The aim of the study was to evaluate electric pacing field of transesophageal left atrial (LA) pacing and BV pacing with 3D heart rhythm simulation. Bipolar right atrial (RA), right ventricular (RV), LV electrodes and multipolar hemispherical esophageal LA electrodes were modeled with CST (Computer Simulation Technology, Darmstadt). Electric pacing field were simulated with bipolar RA and RV pacing with Solid S (Biotronik) electrode, bipolar LV pacing with Attain 4194 (Medtronic) electrode and bipolar LA pacing with TO8 (Osypka) esophageal electrode. 3D heart rhythm model with esophagus allowed electric pacing field simulation of 4-chamber pacing with bipolar intracardiac RA, RV, LV pacing and bipolar transesophageal LA pacing. The pacing amplitudes were 3V RA pacing amplitude, 50V LA pacing amplitude, 1.5V RV pacing amplitude and 3V LV pacing amplitude with 0.5ms pacing pulse duration. The atrioventricular delay between RA pacing and BV pacing was 140ms atrioventricular pacing delay and simultaneous RV and LV pacing. Electric pacing fields were simulated during the different pacing modes AAI, VVI, DDD and DDD0V. The intracardiac far-field pacing potentials were evaluated with intracardiac electrodes and a distance of 1mm from the electrodes with RA electrode 1.104V, RV electrode 0.703V and LV electrode 1.32V. The transesophageal far-field pacing potential was evaluated with transesophageal electrode and a distance of 10mm from the elelctrode with LA electrode 6.076V. Heart rhythm model simulation with esophagus allows evaluation of electric pacing fields in AAI, VVI, DDD, DDD0V and DDD0D pacing modes. Electric pacing field of RA, RV and LV pacing in combination with LA pacing may additional useful pacing mode in CRT non-responders.

Time-dependent cervical vagus nerve stimulation and frequency-dependent right atrial pacing mediates induction of atrial fibrillation.

Objective:This study aimed to investigate the effects of right cervical vagus trunk simulation (RVTS) and/or right atrial pacing (RAP) on the induction of atrial fibrillation (AF).Methods:Twenty-four healthy adult dogs were randomly divided into four groups: RAP groups comprising RAP500 (RAP with 500 beats/min) and RAP1000 (RAP with 1000 beats/min) and RVTS groups comprising RVTS and RAP500+RVTS. All dogs underwent 12-h intermittent RAP and/or RVTS once every 2 h. The AF induction rate, AF duration, atrial effective refractory period (ERP), and dispersion of ERP (dERP) were compared after every 2 h of RAP or/and RVTS.Results:All groups had successful AF induction. The RAP1000 group had the highest AF induction rate and the longest AF duration. The RAP1000 group also had a shortened ERP in comparison to the other groups as well as the maximum dERP. Compared to the RAP500 group, RAP500+RVTS had an increased capacity to induce AF as measured by the AF induction rates, AF duration, ERP, and dERP.Conclusion:Increased tension in the vagus nerve and the intrinsic cardiac autonomic nervous system plays an important role in AF induction through different potential mechanisms. Interventions involving the vagus nerve and/or intrinsic cardiac autonomic nervous system can be a future potential therapy for AF.

Differential Effects of Left Ventricular Pacing Sites on Regional Contraction Patterns and Global Performance.

To define the differential effect of site-specific ventricular counterpacing efficacy during cardiac resynchronization therapy (CRT) to identify the most informative imaging views to quantify it. Cross-sectional and long-axis views commonly are used to assess left ventricular (LV) contractility. The effects of LV apical (LVa) and free-wall (LVfw) pacing during CRT on long- and short-axis contraction, cardiac output, and stroke work were assessed in an open-chested acute canine model to determine whether LVa and LVfw would induce earlier apical than basilar LV radial contraction and earlier free-wall than septal contraction, respectively. Apical (CRTa) and free-wall (CRTfw) using right ventricular (RV) pacing-induced dyssynchrony also were examined. University large animal research laboratory. Ten acutely anesthetized and instrumented open-chested purpose-bred dogs. RV pacing served as the model of cardiac dyssynchrony. Selective LVfw and LVa pacing alone or with RV (CRTfw and CRTa, respectively) were studied relative to right atrial pacing (RA) as the control. Two pairs of 3 ultrasonic crystals were place along the LV longitudinal axis-apex and mid-to-base pairs along septal and free wall lines. Conductance catheter-defined longitudinal LV segmental volumes and pressure-volume data were collected. RV decreased cardiac output and stroke work compared with RA (2.0±0.3 v 1.4±0.1 L/min; 137±22 v 60±14 mJ; p<0.05, respectively). LVfw but not LVa decreased stroke work (130±35 mJ), and CRTa but not CRTfw improved both (2.1±0.2 L/min; 113±13 mJ; p<0.01 v RV pacing). No difference in time to minimal length free wall-to-septal crystal was seen with pacing. Both LVa and CRTa displayed increased apical-to-basilar shortening delay compared with RA, RV, and LVfw (42±47, 9±105, and 1±46 msec, respectively; p<0.05). No matching regional LV volume changes were seen during LVa. LV functional analysis from only a cross-sectional plane may be insufficient to characterize improved LV contraction synchrony during multisite CRT.

Speckle-tracking echocardiography elucidates the effect of pacing site on left ventricular synchronization in the normal and infarcted rat myocardium.

BackgroundRight ventricular (RV) pacing generates regional disparities in electrical activation and mechanical function (ventricular dyssynchrony). In contrast, left ventricular (LV) or biventricular (BIV) pacing can improve cardiac efficiency in the setting of ventricular dyssynchrony, constituting the rationale for cardiac resynchronization therapy (CRT). Animal models of ventricular dyssynchrony and CRT currently relay on large mammals which are expensive and not readily available to most researchers. We developed a methodology for double-site epicardial pacing in conscious rats. Here, following post-operative recovery, we compared the effects of various pacing modes on LV dyssynchrony in normal rats and in rats with ischemic cardiomyopathy.MethodsTwo bipolar electrodes were implanted in rats as follows: Group A (n = 6) right atrial (RA) and RV sites; Group B (n = 7) RV and LV sites; Group C (n = 8) as in group B in combination with left coronary artery ligation. Electrodes were exteriorized through the back. Following post-operative recovery, two-dimensional transthoracic echocardiography was performed during pacing through the different electrodes. Segmental systolic circumferential strain (Ecc) was used to evaluate LV dyssynchrony.ResultsIn normal rats, RV pacing induced marked LV dyssynchrony compared to RA pacing or sinus rhythm, as measured by the standard deviation (SD) of segmental time to peak Ecc, SD of peak Ecc, and the average delay between opposing ventricular segments. LV pacing and, to a greater extend BIV pacing diminished the LV dyssynchrony compared to RV pacing. In rats with extensive MI, the effects of LV and BIV pacing were markedly attenuated, and the response of individual animals was variable.ConclusionsRodent cardiac pacing mimics important features seen in humans. This model may be developed as a simple new tool to study the pathophysiology of ventricular dyssynchrony and CRT.

Frequency-dependent left ventricular performance in women and men

We aimed to determine whether sex differences in humans extend to the dynamic response of the left ventricular (LV) chamber to changes in heart rate (HR). Several observations suggest sex influences LV structure and function in health; moreover, this physiology is also affected in a sex-specific manner by aging. Eight postmenopausal women and eight similarly aged men underwent a cardiac catheterization-based study for force-interval relationships of the LV. HR was controlled by right atrial (RA) pacing, and LV +dP/dt(max) and volume were assessed by micromanometer-tipped catheter and Doppler echocardiography, respectively. Analysis of approximated LV pressure-volume relationships was performed using a time-varying model of elastance. External stroke work was also calculated. The relationship between HR and LV +dP/dt(max) was expressed as LV +dP/dt(max) = b + mHR. The slope (m) of the relationship was steeper in women compared with men (11.8 ± 4.0 vs. 6.1 ± 4.1 mmHg·s(-1)·beats(-1)·min(-1), P = 0.01). The greater increase in contractility in women was reproducibly observed after normalizing LV +dP/dt(max) to LV end-diastolic volume (LVVed) or by measuring end-systolic elastance. LVVed and stroke volume decreased more in women. Thus, despite greater increases in contractility, HR was associated with a lesser rise in cardiac output and a steeper fall in external stroke work in women. Compared with men, women exhibit greater inotropic responses to incremental RA pacing, which occurs at the same time as a steeper decline in external stroke work. In older adults, we observed sexual dimorphism in determinants of LV mechanical performance.

Electrogram analysis at the His bundle region and the proximal coronary sinus as a tool to predict left atrial origin of focal atrial tachycardias

Early activation at the His bundle (HB) region or proximal coronary sinus (CS) during focal atrial tachycardias (FATs) often necessitates biatrial mapping. Analysis of CS electrograms (EGMs) consisting of a near-field (N) component from CS musculature and a far-field (F) component from left atrial (LA) myocardium can uncover LA activation preceding right atrial (RA) activation. A similar pattern might be observed at the HB. Eight patients underwent RA and LA pacing testing the hypothesis that N and F components originating from the RA and LA septum are present in the HB atrial EGM (Pacing group). In this group N preceded F (N-F sequence) in all, while F preceded N (F-N sequence) in seven of eight patients during RA and LA pacing, respectively. Twenty-seven patients with FAT demonstrating earliest activation at the HB or proximal CS during limited RA mapping were also studied (FAT group). Two observers analysed the EGMs at the earliest site during FAT. They found an N-F sequence in 17 (94%) and 16 (89%) of 18 RA FAT and an F-N sequence in seven (78%) and eight (89%) of nine LA FAT, respectively. The F-N sequence predicted the need for LA access with a sensitivity of 78 and 89% and a specificity of 94 and 89%. Near-field and F components from RA and LA activation can be identified in the HB atrial EGM. Earliest atrial EGM analysis at the HB or CS can predict the need for LA access during FAT ablation.

Microvolt T-Wave Alternans in Patients with a Biventricular Implantable Defibrillator

Background/Aim: Microvolt T-wave alternans (MTWA) has been found to be associated with cardiac electrical instability. The aim of this study was to investigate the effects of biventricular pacing on MTWA in comparison with other pacing modalities. Methods : The study group consisted of 50 patients with dilated or ischemic cardiomyopathy with a cardiac resynchronization therapy device. MTWA was measured during several pacing modalities. Results : Overall, 181 MTWA studies were performed in 50 patients. Seventy-nine studies (44%) were negative, 81(45%) were positive and 21 (12%) were indeterminate. With right atrial (RA) pacing, 45% of the MTWA tests were negative. With right ventricular (RV) pacing, 30 % were negative, with left ventricular (LV) pacing 44 % were negative and with biventricular pacing 52% of the tests were negative (P=0.15). The results of TWA testing were concordant between RA pacing and biventricular pacing (K=0.46, P=0.007). Conclusion : MTWA during biventricular pacing correlates with MTWA during atrial pacing and left ventricular pacing.

Biventricular Endocardial Pacing Is Superior to Triventricular Epicardial Pacing in an Ischemic Canine Heart Failure Model

Introduction: Left ventricular (LV) endocardial (Endo) and triventricular (TriV) epicardial (Epi) pacing have been proposed as an alternatives to biventricular (BiV) pacing for cardiac resynchronization therapy (CRT) but it is unknown which is approach is superior. We determined which approach most improved hemodynamics in ischemic canines with heart failure. Methods: The left bundle branch was ablated in 7 canines and epicardial electrodes were placed at 4 sites. Multiple microemoblizations were performed until LV ejection fraction reduced to less than 35%. A right atrial (RA) and right ventricular (RV) were implanted. An atrial transseptal Endo lead was placed at the 4 sites. LV dP/dtmax was measured during BiV Endo, BiV Epi and TriV Epi at 3 AV delays. Percent change from RA pacing was calculated and the greatest improvement with each approach was compared with repeated measures ANOVA. Results: BiV Endo pacing increased dP/dtmax more than BiV Epi and TriV Epi pacing (26.1±11.6% vs. 20.7±10.5% and 22.7±9.2%, p<.05). There was no significant difference between BiV Epi and TriV Epi pacing. Conclusion: BiV Endo pacing was superior to BiV Epi and TriV Epi pacing. BiV Endo pacing is a promising approach to improve CRT and does not require additional leads. Further exploration of Endo pacing in humans is warranted.

Left ventricular systolic torsion correlates global cardiac performance during dyssynchrony and cardiac resynchronization therapy

Left ventricular (LV) systolic torsion is a primary mechanism contributing to stroke volume (SV). We hypothesized that change in LV torsion parallels changes in global systolic performance during dyssynchrony and cardiac resynchronization therapy (CRT). Seven anesthetized open chest dogs had LV pressure-volume relationship. Apical, basal, and mid-LV cross-sectional echocardiographic images were studied by speckle tracking analysis. Right atrial (RA) pacing served as control. Right ventricular (RV) pacing simulated left bundle branch block. Simultaneous RV-LV free wall and RV-LV apex pacing (CRTfw and CRTa, respectively) modeled CRT. Dyssynchrony was defined as the time difference in peak strain between earliest and latest segments. Torsion was calculated as the maximum difference between the apical and basal rotation. RA pacing had minimal dyssynchrony (52 ± 36 ms). RV pacing induced dyssynchrony (189 ± 61 ms, P < 0.05). CRTa decreased dyssynchrony (46 ± 36 ms, P < 0.05 vs. RV pacing), whereas CRTfw did not (110 ± 96 ms). Torsion during baseline RA was 6.6 ± 3.7°. RV pacing decreased torsion (5.1 ± 3.6°, P < 0.05 vs. control), and reduced SV, stroke work (SW), and dP/dt(max) compared with RA (21 ± 5 vs. 17 ± 5 ml, 252 ± 61 vs. 151 ± 64 mJ, and 2,063 ± 456 vs. 1,603 ± 424 mmHg/s, respectively, P < 0.05). CRTa improved torsion, SV, SW, and dP/dt(max) compared with RV pacing (7.7 ± 4.7°, 23 ± 3 ml, 240 ± 50 mJ, and 1,947 ± 647 mmHg/s, respectively, P < 0.05), whereas CRTfw did not (5.1 ± 3.6°, 18 ± 5 ml, 175 ± 48 mJ, and 1,699 ± 432 mmHg/s, respectively, P < 0.05). LV torsion changes covaried across conditions with SW (y = 0.94x+12.27, r = 0.81, P < 0.0001) and SV (y = 0.66x+0.91, r = 0.81, P < 0.0001). LV dyssynchrony changes did not correlate with SW or SV (r = -0.12, P = 0.61 and r = 0.08, P = 0.73, respectively). Thus, we conclude that LV torsion is primarily altered by dyssynchrony, and CRT that restores LV performance also restores torsion.

Linear Ablation of Right Atrial Free Wall Flutter: Demonstration of Bidirectional Conduction Block as an Endpoint Associated With Long‐Term Success

Ablation for atypical atrial flutter (AFL) is often performed during tachycardia, with termination or noninducibility of AFL as the endpoint. Termination alone is, however, an inadequate endpoint for typical AFL ablation, where incomplete isthmus block leads to high recurrence rates. We assessed conduction block across a low lateral right atrial (RA) ablation line (LRA) from free wall scar to the inferior vena cava (IVC) or tricuspid annulus in 11 consecutive patients with atypical RA free wall flutter. LRA block was assessed following termination of AFL, by pacing from the ablation catheter in the low lateral RA posterior to the ablation line and recording the sequence and timing of activation anterior to the line with a duodecapole catheter, and vice versa for bidirectional block. LRA block resulted in a high to low activation pattern on the halo and a mean conduction time of 201 +/- 48 ms to distal halo. LRA conduction block was present in only 2 out of 6 patients after termination of AFL by ablation. Ablation was performed during sinus rhythm (SR) in 9 patients to achieve LRA conduction block. No recurrence of AFL was observed at long-term follow-up (22 +/- 12 months); 3 patients developed AF. Termination of right free wall flutter is often associated with persistent LRA conduction and additional radiofrequency ablation (RFA) in SR is usually required. Low RA pacing may be used to assess LRA conduction block and offers a robust endpoint for atypical RA free wall flutter ablation, which results in a high long-term cure rate.